Many snakes rely on blending in. Venomous ones are more likely to do the opposite. Across more than 450 species, venomous snakes stood out more against their natural surroundings than harmless ones, researchers at the University of Galway in Ireland report in the Journal of Animal Ecology.
Biologists call bright colors that warn predators away aposematism. Poison dart frogs and wasps are classic examples. For snakes, the link between venom and warning colors had not been tested across so many species.
Thousands of photos
The team, led by Amy Duclaux, used thousands of photographs from iNaturalist, a site where people share pictures of wildlife they see. That let the researchers judge each snake against the kind of background it actually lives on, not against a lab wall.
Venomous species were clearly more visually distinct from their habitats. Red and yellow were "particularly effective" at making a snake stand out, according to the study.
"Some venomous snakes appear to advertise that they're dangerous," Duclaux says.
Not a rule
The pattern is a tendency, not a law. Many venomous snakes are not brightly colored at all and still rely on camouflage, the authors note. And some harmless snakes copy the colors of dangerous ones.
The study supports the idea that venom and warning colors evolved together in some lineages. A bright snake is not always a venomous one, and a dull one is not always safe.
